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Re: Timber pitched roof as a Diaphragm

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-----Original Message-----
From: Tarek Mokhtar <Tarek(--nospam--at)>
To: seaoc(--nospam--at) <seaoc(--nospam--at)>
Date: Sunday, January 18, 1998 11:07 AM
Subject: Re: Timber pitched roof as a Diaphragm

>I am not aware of any software for this application.
>my personal opinion is that diapragms do not really
>work for pitches over 6:12 unless you prvide a line
>of bracing close to the ridge line.
>my 2 cents worth.
>Tarek Mokhtar
>consulting engineer

 Thanks for the response Tarek.  I am of similar opinion and I normally
specify a diaphragm or braced connection at or near the ridge line.  The
problem becomes difficult where the ceiling is to be vaulted.  As a further
analytical tool for large roofs what do you think of using analyses like
that used for steel deck design?  Or using thin shell analyses?

Rigidity of the roof as a whole under limit states conditions would be a
concern no doubt and it appears from simple models such as a folded piece of
cardboard or paper that a diaphragm at the gable ends (if present) would
stiffen the assembly (?).

Thor Tandy P.Eng
Victoria BC